Info on the QCS website indicates the SL-70 uses a dual boiler with a brass boiler for brewing and a thermoblock for steam.
Cut and pasted from the QCS webpage describing the SL-70 and SL-90 (I added the underlining):
Features include an integrated coffee tamper, a large cup storage area which can be heated up on the SL 90 model(shown at right) and a vertically adjustable cup tray. Swivel steam and hot water nozzle with finger protection. But wait, there is more!
- Metal housing
- High performance pump providing pressure of up to 19 bar - Thermal block heater with special SOLIS brewing system for optimum froth
- Large capacity water reservoir
- Large storage plate for cups
- Height adjustable drip tray
- Control panel with rocker-switches and diodes
- Swivel steam and hot water nozzle with saftey grip
- Filter holder and inserts for 1 or 2 cups
- Special filter for pods
- Swivel hot water and steam nozzle with safety grip for hot drinks and milk frothing -(280psi) pressure, which guarantees perfect aroma extraction from the coffee powder - Heavy-duty brass boiler assures optimum brewing temperature
- Solid brass portafilter helps retain heat during the brewing process